About 20 supporters of an environmental activist detained in Malaysia have staged a protest outside the Australian headquarters of the rare-earth mining company she was targeting when she was arrested.

Natalie Lowrey, a New Zealand citizen and permanent resident of Australia living in Bondi, was arrested on Sunday outside of a rare earth processing plant in the eastern state of Pahang.

The plant near Kuantan began operating last year and is owned by the Australian company Lynas Corporation, but environmental activists claim it produces toxic waste.

Despite 15 Malaysian citizens also being arrested during what they say was a 1,000-strong protest, only Lowrey remains in jail.

Fellow activists gathered outside Lynas’s headquarters in Sydney on Friday to show their support for Natalie and to call on Malaysia to release her.

Among them was Holly Creenaune, who has known Lowrey for 10 years.

“I spoke to a friend of hers over there with her this morning, and she is still being held and doesn’t know what she is being charged with,” Creenaune said.

Tully McIntyre, a fellow activist in Malaysia with Lowrey, says she is now able to phone home and is being treated well.

“Natalie is a strong woman, she really is, and she is aware of the worst case scenario,” McIntyre said.

Malaysian-based environmental activists held a candlelight vigil for Lowrey on Thursday night.

The Australian government said it would not comment on Lowrey’s case. She faces two years in jail if charged and found guilty.

“As Ms Lowrey is a New Zealand citizen, we have no on-the-record comment on this matter,” a spokeswoman for the Department of Foreign Affairs and Trade said on Friday in response to questions about what support, if any, the Australian government could offer.

On Thursday, Kuantan district police chief, assistant commissioner Abdul Aziz Salleh, told Guardian Australia the police investigation into Lowrey was complete and now in the hands of prosecutors.

“There are two very wrong and obvious things she has done,” Abdul Aziz said.

“We have recommended that she be charged under the Immigration Act, and that she also be charged for unlawful assembly.”

He confirmed the latter charge carried a maximum two-year jail term, a fine, or both.